1. Field of the Invention
The present invention relates to a pantagraph-type jack and, in particular, an improved pantagraph-type jack, in which outer ends of a pair of lower arms disposed in a V-shaped manner whose inner ends are swingably connected to a base and outer ends of a pair of upper arms disposed in an inverted V-shaped manner whose inner ends are swingably connected to a load bearing platform are connected via first and second connecting shafts, and a threaded rod supported on the first connecting shaft in a rotatable but axially non-movable manner is screwed into a threaded bore provided in the second connecting shaft.
2. Description of the Prior Art
Such a pantagraph-type jack is already known as disclosed in, for example, Japanese Patent Publication No. 3-6120.
In such a pantagraph-type jack of the art, the degree of lift of the load bearing platform is increased by increasing the lengths of the lower arms, the upper arms and the threaded rod. However, when the lengths of the lower arms, the upper arms and the threaded rod are increased, the size of the jack increases and thus it is difficult to store it in a small storage space in an automobile, etc.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an objective of the present invention to provide a compact pantagraph-type jack in which the degree of lift of the load bearing platform can be increased without increasing the lengths of the lower arms, the upper arms and the threaded rod.
In order to achieve the above-mentioned objective, the present invention provides firstly a pantagraph-type jack in which outer ends of a pair of lower arms disposed in a V-shaped manner whose inner ends are swingably connected to a base and outer ends of a pair of upper arms disposed in an inverted V-shaped manner whose inner ends are swingably connected to a load bearing platform are connected via first and second connecting shafts, and a threaded rod supported on the first connecting shaft in a rotatable but axially non-movable manner is screwed into a threaded bore provided in the second connecting shaft, wherein the base comprises an upper base member and a lower base member which are connected to each other relatively movably in a vertical direction, inner ends of the pair of lower arms are swingably connected to the upper base member via a pair of lower pivots arranged in a horizontal direction, lower sector gears are formed on outer peripheries of the inner ends of the two lower arms, and a lower rack which meshes with the lower sector gears is disposed in the vertical direction and secured on the lower base member.
In accordance with the above-mentioned first feature, when the threaded rod is rotated in a clockwise direction so as to erect each pair of lower arms and upper arms around the lower pivots and the upper pivots respectively in order to erect the collapsed or contracted jack, since the lower sector gears formed on the outer peripheries of the inner ends of the two lower arms rotate at the same time so as to ascend the lower racks, the upper base member having the lower pivots lifts relative to the lower base member having the lower racks. Therefore, the total amount of lift of the jack becomes the sum of the amount of lift of the load bearing platform due to the erection of the lower arms and the upper arms and the amount of lift of the upper base member relative to the lower base member, and thus the amount of lift can be increased in comparison with a jack of the prior art in which the amount of lift of the load bearing platform is determined only by the erection of the lower arms and the upper arms. Moreover, since it is unnecessary to specially increase the lengths of the lower arms, the upper arms and the threaded rod, the size of the jack is not made larger.
The present invention provides secondly a pantagraph-type jack in which the outer ends of a pair of lower arms disposed in a V-shaped manner whose inner ends are swingably connected to a base and outer ends of a pair of upper arms disposed in an inverted V-shaped manner whose inner ends are swingably connected to a load bearing platform are connected via first and second connecting shafts, and a threaded rod supported on the first connecting shaft in a rotatable but axially non-movable manner is screwed into a threaded bore provided in the second connecting shaft, wherein the load bearing platform comprises a lower load bearing platform member and an upper load bearing platform member which are connected to each other relatively movably in a vertical direction, inner ends of the pair of upper arms are swingably connected to the lower load bearing platform member via a pair of upper pivots arranged in the horizontal direction, upper sector gears are formed on the outer peripheries of the inner each of the two upper arms and an upper rack which meshes with the upper sector gears is disposed in the vertical direction and secured on the upper load bearing platform member.
In accordance with the above-mentioned second feature, when the threaded rod is rotated in the clockwise direction so as to erect each pair of lower arms and upper arms around the lower pivots and the upper pivots respectively in order to erect the collapsed jack, since the upper sector gears formed on the outer peripheries of the inner ends of the two upper arms rotate at the same time so as to push up the upper racks, the upper load bearing platform member having the racks lifts relative to the lower load bearing platform member having the upper pivots. Therefore, the total amount of lift of the jack becomes the sum of the amount of lift of the load bearing platform due to the erection of the lower arms and the upper arms and the amount of lift of the upper load bearing platform member relative to the lower load bearing platform member, and thus the amount of lift can be increased in comparison with a jack of the prior art in which the amount of lift of the load bearing platform is determined only by the erection of the lower arms and the upper arms. Moreover, since it is unnecessary to specially increase the lengths of the lower arms, the upper arms and the threaded rod, the size of the jack is not made larger.
The present invention further provides a pantagraph-type jack in which outer ends of a pair of lower arms disposed in a V-shaped manner whose inner ends are swingably connected to a base and outer ends of a pair of upper arms disposed in an inverted V-shaped manner whose inner ends are swingably connected to a load bearing platform are connected via first and second connecting shafts, and a threaded rod supported on the first connecting shaft in a rotatable but axially non-movable manner is screwed into a threaded bore provided in the second connecting shaft, wherein the base comprises an upper base member and a lower base member which are connected to each other relatively movably in a vertical direction, inner ends of the pair of lower arms are swingably connected to the upper base member via a pair of lower pivots arranged in a horizontal direction, lower sector gears are formed on outer peripheries of the inner ends of the two lower arms, and a lower rack which meshes with the lower sector gears is disposed in the vertical direction and secured on the lower base member, and the load bearing platform comprises a lower load bearing platform member and an upper load bearing platform member which are connected to each other relatively movably in a vertical direction, inner ends of the pair of upper arms are swingably connected to the lower load bearing platform member via a pair of upper pivots arranged in the horizontal direction, upper sector gears are formed on the outer peripheries of the inner ends of the two upper arms, and an upper rack which meshes with the upper sector gears is disposed in the vertical direction and secured on the upper load bearing platform member.
In accordance with the above-mentioned third feature, when the threaded rod is rotated in a clockwise direction so as to erect each pair of lower arms and upper arms around the lower pivots and the upper pivots respectively in order to erect the collapsed jack, since the lower sector gears formed on the outer peripheries of the inner ends of the lower arms rotate at the same time so as to ascend the lower racks, the upper base member having the lower pivots lifts relative to the lower base member having the lower racks, and since the upper sector gears formed on the outer peripheries of the inner ends of the upper arms rotate at the same time so as to push up the upper racks, the upper load bearing platform member having the racks lifts relative to the lower load bearing platform member having the upper pivots. Therefore, the total amount of lift of the jack becomes the sum of the amount of lift of the load bearing platform due to the erection of the lower arms and the upper arms, the amount of lift of the upper base member relative to the lower base member and the amount of lift of the upper load bearing platform member relative to the lower load bearing platform member, and thus the amount of lift can be increased to a great extent in comparison with a jack of the prior art in which the amount of lift of the load bearing platform is determined only by the erection of the lower arms and the upper arms. Moreover, since it is unnecessary to specially increase the lengths of the lower arms and the upper arms, the size of the jack is not made larger.
In addition to any one of the first to the third features, the present invention fourthly provides a pantagraph-type jack, wherein the rack comprises a plurality of pins which are inserted in a vertical array on the corresponding one of the lower base member and upper load bearing platform members, and both sides of these pins are made to mesh with a corresponding pair of sector gears.
In accordance with the above-mentioned fourth feature, one rack which is shared by a corresponding pair of sector gears will suffice and thus the arrangement can be simplified.
The above-mentioned objectives, other objectives, characteristics and advantages of the present invention will become apparent from an explanation of a preferable embodiment which will be described in detail below by reference to the attached drawings.